Field of the Invention
The invention relates to the field of in vitro fertilization (IVF), which is a process by which mammalian egg cells are fertilized by sperm outside the womb. More particularly, evaluation of a secretome profile is used to enhance the pregnancy success rate when the fertilized egg is implanted into a patient's uterus.
Description of the Related Art
IVF infertility treatment offers infertile couples a chance to have a biologically related child. IVF may overcome female infertility due to problems of the fallopian tube or endometriosis. IVF also overcomes male infertility due to problems with sperm quality or quantity. The IVF process involves hormonally controlling the ovulatory process, removing eggs (termed ova) from the woman's ovaries and permitting the sperm to fertilize the eggs in a fluid medium. The fertilized egg, termed an embryo, is subsequently transferred to the patient's uterus with the intent of establishing a successful pregnancy. Due to expensive procedural costs, IVF is only attempted after the failure of less expensive fertility treatments.
FIG. 1 displays a schematic for mammalian blastocyst implantation. Mammalian embryo implantation is a complex and intricate process involving numerous biological changes at both the embryo and endometrial level. The interaction between the blastocyst and the endometrium is a function of both a receptive endometrial environment and a healthy blastocyst. A blastocyst failing to implant or an endometrium failing to sustain growth and differentiation will result in spontaneous abortion. The prior art teaches very little about the embryo's role in the events leading to the attachment of a viable blastocyst to a receptive uterine luminal epithelium.
IVF treatment begins with administration of hormonal medications to stimulate ovarian follicle production, such as gonadotropins hormones. The prevention of spontaneous ovulation involves using other hormones, such as GnRH antagonists or GnRH agonists that block the natural surge of luteinizing hormone. With adequate follicular maturation, administration of human chorionic gonadotropin hormone causes ovulation approximately 42 hours after the administration. However, the egg retrieval procedure takes place just prior to ovulation, in order to recover the eggs from the ovary. The egg retrieval proceeds using a transvaginal technique involving an ultrasound-guided needle that pierces the vaginal wall to reach the ovaries. After recovery of the follicles through the needle, the follicular fluid is provided to the IVF laboratory to identify eggs. Typically, the procedure retrieves between 10 and 30 eggs. The retrieval procedure takes approximately 20 minutes and is usually done under conscious sedation or general anesthesia.
For IVF, the fertilization of the egg (termed insemination) proceeds in the laboratory where the identified eggs and semen are usually incubated together in a culture media. The confirmation of fertilization proceeds by monitoring the eggs for cell division. For instance, a fertilized egg may show two pronuclei. In certain situations, such as low sperm count or motility, a single sperm may be injected directly into the egg using a method called intracytoplasmic sperm injection (ICSI). In another option known as gamete intrafallopian transfer, eggs are removed from the woman and placed in one of the fallopian tubes, along with the man's sperm. In this example, fertilization occurs within the women's body, a process termed in vivo fertilization.
Selected embryos are transferred to the patient's uterus through a thin, plastic catheter, which goes through the vagina and cervix. Typically, transfer of 6-8 cell stage embryos to the uterus occurs three days after embryo retrieval. Alternatively, embryos can be placed into an extended culture system with a transfer done at the blastocyst stage at approximately five days post-retrieval. Blastocyst stage transfers often result in higher pregnancy rates. Additionally, embryonic cryopreservation, or the storage of embryos in a frozen state, is feasible until uterine transfer. For example, the first term pregnancy derived from a frozen human embryo was reported in 1984.
Despite progressively improving IVF pregnancy rates, the majority of transferred human embryos result in implantation failure. For example, Canadian clinics reported an average pregnancy rate of 35% for one cycle, but a live birth rate of only 27% in 2006. Moreover, implantation success rates may decrease with the increasing maternal age, if donor eggs are not used. Various factors are associated with implantation failure, including embryo chromosome aneuploidies related to advanced maternal age and maternal factors such as endometrium response failure to hormone regulation.
To overcome low implantation success rate, multiple embryos are commonly transferred during a single IVF procedure. The process for selecting embryos for transfer often involves grading methods developed in individual laboratories to judge oocyte and embryo quality. An arbitrary embryo score, involving the number and quality of embryos, may reveal the probability of pregnancy success post-transfer. For example, an embryologist may grade embryos using morphological qualities including the number of cells, clearness of cytoplasm, evenness of growth and degree of fragmentation. However, embryo selection based on morphological qualities is not precise. Often, several embryos selected for these general qualities are implanted to improve the chance of pregnancy. The number of embryos transferred depends upon the number available, the age of the woman and other health and diagnostic factors.
The transfer of multiple embryos, however, often results in multiple pregnancies, a major complication of IVF. In general, multiple pregnancies, specifically, more than twins, hold maternal and fetal risks. For example, multiple births are associated with increased risk of pregnancy loss, neonatal morbidity, obstetrical complications, and prematurity with potential for long term damage. Some countries implemented strict limits on the number of transferred embryos to reduce the risk of high-order multiples (e.g., triplets or more). However, these limitations are not universally followed or accepted.